Hm... but I guess they could overwrite the UK firmware with the US firmware using the updater (and the "version changing" updater hack) and then flash the Reader with igorsk's flasher. That should work.

I know of at least one user who did just that. He posted in the PRSCustomizer thread and reported no problems. If I had to guess, it's nothing more than a version number change. What will be interesting is if people who do this can still buy books